The invention relates to an x-ray examination apparatus comprising an examination table, a patient support platform resting on the examination table, an x-ray source with a remote-controllable collimator (or diaphragm) restricting the radiation beam, a longitudinal transport carriage movable along the length of the patient support platform, and a cassette drawer insertable into the longitudinal transport carriage, with clamping jaws for the purpose of support-mounting the insertable x-ray film cassette.
From the German Offenlegungsschrift No. 22 57 778, a control installation for the restriction of the effective radiation beam of an x-ray tube is known wherein, pursuant to insertion of an x-ray film cassette into the cassette receptacle of an x-ray examination apparatus, two continuously variable transducers installed in the cassette receptacle, are adjusted upon displacement of the clamping jaws. The one of the two transducers is adjusted by the two clamping jaws measuring the width of the x-ray film cassette, and the other transducer is adjusted by the clamping jaws measuring the length of the x-ray film cassette. These two transducers are connected to a control circuit by means of which the collimator and thus also the useful radiation beam are adjusted corresponding to the scanned cassette dimensions. In the case of this control installation, it is considered disadvantageous that the cassette receptacle, due to the electric connections of the transducers, can no longer be removed during fluoroscopy. Accordingly, in the case of this x-ray examination apparatus, the cassette receptacle must be pushed out in the direction of the table length from the fluoroscopy region during fluoroscopy. The cassette receptacle remains beneath the patient support and thus obstructs the adjustability of the fluoroscopy installation in the direction of the table length.
The U.S. Pat. No. 3,986,034 discloses a cassette support drawer insertable beneath the patient support wherein one of the clamping jaws, engaging the inserted x-ray film cassette, is connected, via a lever and a cable, with a magnet which is adjustable transversely to the insert direction in the cassette drawer. The discrete positions of the magnet allocated to the different cassette dimensions are associated with reed contacts on the longitudinal transport carriage. The latter reed contacts adjust the collimator of the x-ray examination apparatus corresponding to the dimensions of the inserted x-ray film cassette. In the case of this device, the cassette drawer can, indeed, be removed from the examination table. However, it is considered disadvantageous that this device functions only in the case of specified predetermined discrete cassette dimensions. In particular, this device does not satisfy the increased safety regulations in some countries which require the correct collimation (or diaphragming-in) function in the case of random cassette dimensions and not only in the case of standardized cassette sizes.